All The Ways Zika Virus Spreads

All the Ways You Can (& Cannot) Get Zika Virus

This story was originally published on February 5, 2016 and has been updated throughout.

Another day, another possible way to catch the Zika virus. Or at least that’s what it feels like. UPDATE (March 8, 2016): Today, the World Health Organization (WHO) announced after an emergency committee meeting on the virus that sexual transmission is a bigger threat than we thought, the Associated Press reported. The experts came to this conclusion after looking at reports from several countries.

Ever since Zika started spreading across the Western Hemisphere, experts have focused on the threat posed by mosquitoes — which is by far the most likely way to come down with the infection. But with back-to-back reports of people catching the virus through sex and blood transfusions, and news that Brazilian health officials have found "active Zika virus" in saliva and urine samples, this situation just keeps getting scarier by the day.

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Also not helpful are the conspiracy theories circulating out there, blaming bioterrorism, the Tdap vaccine, or some kind of ploy to pad the pockets of healthcare companies. No. Ignore those voices. The virus isn’t airborne like the flu; it isn’t spread via handshakes; nor is it a government cover-up that’s straight out of the recent X-Files reboot.

Here’s a no-nonsense guide to what we know about how the virus spreads.

Mosquitoes Experts have said all along that mosquitoes are the number one transmitters of the virus. “They probably account for at least 99% of the cases,” says Peter Hotez, MD, PhD, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston. In the Americas, two species of these pests are known to be able to carry the virus and infect humans: Aedes aegypti, which tend to live in the states bordering the Gulf of Mexico, and Aedes albopictus, which can live farther north, in some Midwestern and Northeastern states.

Here’s what happens: When a mosquito bites a person who’s infected with the virus, that mosquito then carries the virus around with it. If it happens to swing by, say, your backyard barbecue, it can transfer the virus by biting another human host, and the cycle repeats itself. (Experts still aren’t sure exactly how long it can live in the mosquito, but they think it remains in the blood of an infected human for a few days to a week.)

Although four out of five people probably won’t experience any symptoms, that’s not necessarily fantastic news — if you don’t know you have the virus, you might inadvertently pass it on to someone else. For example, let’s say you catch the virus while traveling in a country with a Zika outbreak, but you don’t come down with its telltale symptoms (a mild fever, rash, or joint pain). If that’s the case, you might not bother to wear mosquito repellent or extra long clothing when you’re outdoors, which can up the odds of getting bitten again, and passing the virus along to another hungry bloodsucker.

We should point out that as of right now, no one has caught the virus from a mosquito in the U.S. — only from insects abroad. (So far, one person has been infected with Zika in the states, and that was transmitted sexually. We'll get to that, keep reading.)

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The scariest part of the Zika virus is the link to two things: a rare syndrome called Guillain-Barré syndrome (GBS), a mysterious (but treatable) serious illness that can cause paralysis, and a birth defect called microcephaly, or a smaller-than-average head. Though the virus has been active in various parts of the world for decades, the link to the birth defects was only discovered last year when health officials noticed a surge in cases, while the link to GBS was first reported in 2013. (It's worth noting that experts still aren't certain if Zika is definitively causing either, but there is growingevidence to suggest it.)

If a Zika-infected mosquito bites a pregnant woman, the virus can travel into her bloodstream, and from there, might make its way to the baby, where it may interfere with fetal skull and brain development, says Dr. Hotez. Not every pregnant woman who contracts Zika will give birth to a baby with microcephaly. And there are degrees of severity of the defect as well: Mild cases won’t necessarily cause any health problems, but babies with severe conditions might have seizures and learning disabilities later in life. Currently, there’s no cure or treatment for microcephaly during any stage of the baby’s development; nor, for that matter, is there a cure or vaccine for the Zika virus.

What about breastfeeding? Good news: The Centers for Disease Control and Prevention says there aren’t any reports showing that babies can catch the virus while they’re breastfeeding, so women don’t have to stop on account of Zika.

Sex As early as last week, the idea that Zika could be spread via semen seemed more theoretical than probable. Then, health officials in Dallas County confirmed that a patient in the area contracted the virus after having sexual contact with someone who’d returned from one of the countries with a Zika outbreak. UPDATE (March 8, 2016) And now data from several countries has prompted WHO director-general Margaret Chan, MD, to say, per the Associated Press, "reports and investigations in several countries strongly suggest that sexual transmission of the virus is more common than previously assumed."

In February, the CDC issued a press release stating that, until researchers know more, pregnant women should take some extra precautions. The current advice: If your male partner lives in (or recently traveled to) one of the areas where the Zika virus is circulating, he should either wear a condom — or you two should put off sex entirely — until you give birth. Abstaining from sex for nine months may sound crazy, but because of all the unknowns, the only way to reduce your risk to zero is exactly that. However, it's completely up to you to decide your own tolerance for risk, and if you're not pregnant or actively trying to get pregnant, this is less of a concern.

Blood transfusions Experts have known that this was a possibility, but health officials in Brazil recently confirmed that two people who’d received blood transfusions also became infected with the Zika virus. Even though the odds of this happening are super low, the American Red Cross has asked people not to donate blood if they’ve traveled to Mexico, the Caribbean, or Central or South America within 28 days. (They also say that donors who do give blood and develop symptoms of the virus later on to let them know immediately; they can quarantine your blood.)

Other possibilitiesAs for more ways the virus can spread — like the "active viruses" spotted in saliva and urine — researchers say it's way too early to know if the presence of the virus in those bodily fluids means they could be another way for you to catch it. "So far, there's no evidence of transmission," says Dr. Hotez, "but it needs to be investigated."